package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.Serializable;

/**
 * Encapsulates sort criteria for returned hits.
 * 
 * <p>
 * The fields used to determine sort order must be carefully chosen. Documents
 * must contain a single term in such a field, and the value of the term should
 * indicate the document's relative position in a given sort order. The field
 * must be indexed, but should not be tokenized, and does not need to be stored
 * (unless you happen to want it back with the rest of your document data). In
 * other words:
 * 
 * <p>
 * <code>document.add (new Field ("byNumber", Integer.toString(x), Field.Store.NO, Field.Index.UN_TOKENIZED));</code>
 * </p>
 * 
 * 
 * <p>
 * <h3>Valid Types of Values</h3>
 * 
 * <p>
 * There are four possible kinds of term values which may be put into sorting
 * fields: Integers, Longs, Floats, or Strings. Unless
 * {@link SortField SortField} objects are specified, the type of value in the
 * field is determined by parsing the first term in the field.
 * 
 * <p>
 * Integer term values should contain only digits and an optional preceding
 * negative sign. Values must be base 10 and in the range
 * <code>Integer.MIN_VALUE</code> and <code>Integer.MAX_VALUE</code>
 * inclusive. Documents which should appear first in the sort should have low
 * value integers, later documents high values (i.e. the documents should be
 * numbered <code>1..n</code> where <code>1</code> is the first and
 * <code>n</code> the last).
 * 
 * <p>
 * Long term values should contain only digits and an optional preceding
 * negative sign. Values must be base 10 and in the range
 * <code>Long.MIN_VALUE</code> and <code>Long.MAX_VALUE</code> inclusive.
 * Documents which should appear first in the sort should have low value
 * integers, later documents high values.
 * 
 * <p>
 * Float term values should conform to values accepted by
 * {@link Float Float.valueOf(String)} (except that <code>NaN</code> and
 * <code>Infinity</code> are not supported). Documents which should appear
 * first in the sort should have low values, later documents high values.
 * 
 * <p>
 * String term values can contain any valid String, but should not be tokenized.
 * The values are sorted according to their {@link Comparable natural order}.
 * Note that using this type of term value has higher memory requirements than
 * the other two types.
 * 
 * <p>
 * <h3>Object Reuse</h3>
 * 
 * <p>
 * One of these objects can be used multiple times and the sort order changed
 * between usages.
 * 
 * <p>
 * This class is thread safe.
 * 
 * <p>
 * <h3>Memory Usage</h3>
 * 
 * <p>
 * Sorting uses of caches of term values maintained by the internal HitQueue(s).
 * The cache is static and contains an integer or float array of length
 * <code>IndexReader.maxDoc()</code> for each field name for which a sort is
 * performed. In other words, the size of the cache in bytes is:
 * 
 * <p>
 * <code>4 * IndexReader.maxDoc() * (# of different fields actually used to sort)</code>
 * 
 * <p>
 * For String fields, the cache is larger: in addition to the above array, the
 * value of every term in the field is kept in memory. If there are many unique
 * terms in the field, this could be quite large.
 * 
 * <p>
 * Note that the size of the cache is not affected by how many fields are in the
 * index and <i>might</i> be used to sort - only by the ones actually used to
 * sort a result set.
 * 
 * <p>
 * Created: Feb 12, 2004 10:53:57 AM
 * 
 * @author Tim Jones (Nacimiento Software)
 * @since lucene 1.4
 * @version $Id: Sort.java 598376 2007-11-26 18:45:39Z dnaber $
 */
public class Sort implements Serializable {

	/**
	 * Represents sorting by computed relevance. Using this sort criteria
	 * returns the same results as calling
	 * {@link Searcher#search(Query) Searcher#search()}without a sort criteria,
	 * only with slightly more overhead.
	 */
	public static final Sort RELEVANCE = new Sort();

	/** Represents sorting by index order. */
	public static final Sort INDEXORDER = new Sort(SortField.FIELD_DOC);

	// internal representation of the sort criteria
	SortField[] fields;

	/**
	 * Sorts by computed relevance. This is the same sort criteria as calling
	 * {@link Searcher#search(Query) Searcher#search()}without a sort criteria,
	 * only with slightly more overhead.
	 */
	public Sort() {
		this(new SortField[] { SortField.FIELD_SCORE, SortField.FIELD_DOC });
	}

	/**
	 * Sorts by the terms in <code>field</code> then by index order (document
	 * number). The type of value in <code>field</code> is determined
	 * automatically.
	 * 
	 * @see SortField#AUTO
	 */
	public Sort(String field) {
		setSort(field, false);
	}

	/**
	 * Sorts possibly in reverse by the terms in <code>field</code> then by
	 * index order (document number). The type of value in <code>field</code>
	 * is determined automatically.
	 * 
	 * @see SortField#AUTO
	 */
	public Sort(String field, boolean reverse) {
		setSort(field, reverse);
	}

	/**
	 * Sorts in succession by the terms in each field. The type of value in
	 * <code>field</code> is determined automatically.
	 * 
	 * @see SortField#AUTO
	 */
	public Sort(String[] fields) {
		setSort(fields);
	}

	/** Sorts by the criteria in the given SortField. */
	public Sort(SortField field) {
		setSort(field);
	}

	/** Sorts in succession by the criteria in each SortField. */
	public Sort(SortField[] fields) {
		setSort(fields);
	}

	/**
	 * Sets the sort to the terms in <code>field</code> then by index order
	 * (document number).
	 */
	public final void setSort(String field) {
		setSort(field, false);
	}

	/**
	 * Sets the sort to the terms in <code>field</code> possibly in reverse,
	 * then by index order (document number).
	 */
	public void setSort(String field, boolean reverse) {
		SortField[] nfields = new SortField[] {
				new SortField(field, SortField.AUTO, reverse),
				SortField.FIELD_DOC };
		fields = nfields;
	}

	/** Sets the sort to the terms in each field in succession. */
	public void setSort(String[] fieldnames) {
		final int n = fieldnames.length;
		SortField[] nfields = new SortField[n];
		for (int i = 0; i < n; ++i) {
			nfields[i] = new SortField(fieldnames[i], SortField.AUTO);
		}
		fields = nfields;
	}

	/** Sets the sort to the given criteria. */
	public void setSort(SortField field) {
		this.fields = new SortField[] { field };
	}

	/** Sets the sort to the given criteria in succession. */
	public void setSort(SortField[] fields) {
		this.fields = fields;
	}

	/**
	 * Representation of the sort criteria.
	 * 
	 * @return Array of SortField objects used in this sort criteria
	 */
	public SortField[] getSort() {
		return fields;
	}

	public String toString() {
		StringBuffer buffer = new StringBuffer();

		for (int i = 0; i < fields.length; i++) {
			buffer.append(fields[i].toString());
			if ((i + 1) < fields.length)
				buffer.append(',');
		}

		return buffer.toString();
	}
}
